Flavonoid

Flavonoids were originally referred to as Vitamin P, likely due to the effect they had on the permeability of vascular capillaries, but this term is rarely used now.

According to the IUPAC nomenclature, they can be classified into:

The three flavonoid classes above are all ketone-containing compounds, and as such, are flavonoids and flavonols. This class was the first to be termed "bioflavonoids." The terms flavonoid and bioflavonoid have also been more loosely used to describe non-ketone polyhydroxy polyphenol compounds which are more specifically termed flavanoids, flavan-3-ols (or catechins).